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Fungal Associations - Lichens
Fungal Associations - Lichens
Lichens are composite organisms formed through a mutualistic symbiosis between a fungus (the mycobiont) and a photosynthetic partner (the photobiont), which is typically a green alga or, in some cases, cyanobacteria. Together, they create a unique “super-organism” capable of thriving in environments where neither partner could survive alone.
In this partnership:
The fungus forms the body of the lichen and provides structure, protection, and the ability to absorb minerals and moisture from the environment.
The alga or cyanobacterium contributes carbohydrates and other organic molecules via photosynthesis, supplying energy to both partners.
In lichens with cyanobacteria, an additional benefit exists: the ability to fix atmospheric nitrogen, enriching the surrounding soil.
Approximately 99% of all lichens have a fungal partner belonging to the phylum Ascomycota, with a small minority involving Basidiomycota.
Lichens are very common in certain environments including central Texas. It is not uncommon to find 3-7 species of lichens on the same tree branch. In this image you can see at least 3 species all with different shapes and forms. If you look carefully you can see the cups of two of them indicating that the base fungus involved in the lichen is from the phylum Ascomycota (the cup fungi).
Lab Activity: External Observation of a Live Lichen (Ramalina)
Lab Activity: External Observation of a Live Lichen (Ramalina)
Materials
Materials
Live Ramalina specimen
Dissecting microscope
Note: Handle the specimen gently.
Instructions
Instructions
Place the Ramalina specimen under the dissecting microscope.
Observe the branching fruticose thallus, which forms strap-like or shrubby structures.
Look for small cup-like reproductive structures (apothecia) on the surface of the lichen.
These structures are produced by the fungal partner and contain the spore-producing sacs.
Consider what this structure suggests about the type of fungus that forms this lichen.
Use your observations to answer the worksheet questions.
(Ramalina is a fruticose lichen whose apothecia contain asci and spores produced by the fungal partner.)
Clean Up
Clean Up
Return the specimen to its container.
Turn off the dissecting microscope.
Ecology and Distribution
Ecology and Distribution
Lichens are highly adaptable and can be found worldwide, from arctic tundras to tropical forests. They grow on rocks, tree bark, soil, roofs, tombstones, and other exposed surfaces. To date, scientists have described about 15,000 lichen species, though many more likely exist.
Lichens vary greatly in color—ranging from white, gray, and black to vibrant greens, yellows, browns, and reds. Their pigments not only give lichens distinctive appearances but also protect the photobiont from harmful UV radiation, enabling them to survive in extreme sunlight.
Lichens also play critical ecological roles:
Soil formation – They secrete lichen acids that break down rock, releasing minerals and contributing to the slow buildup of soil.
Nitrogen cycling – Cyanobacteria-containing lichens enrich soils by fixing nitrogen into biologically available compounds.
Environmental indicators – Many lichens are highly sensitive to air pollution and are widely used as bioindicators of ecosystem health.
Adaptations for Survival
Adaptations for Survival
Lichens are remarkably resilient organisms:
They can survive extreme desiccation, remaining dormant for long periods.
When water becomes available (from rain, fog, or dew), they rapidly rehydrate and resume photosynthesis.
A lichen can absorb up to 35 times its weight in water when hydrated.
Due to their slow metabolic rates, many lichens grow only a few millimeters per year. Some individuals may live for centuries—even thousands of years in stable environments.
Body Forms of Lichens
Body Forms of Lichens
Lichens occur in three main morphological forms:
Crustose – Grow as thin, crust-like layers tightly attached to rocks, bark, or soil.
Foliose – Have a leafy, lobed appearance and are only loosely attached to the substrate.
Fruticose – Appear shrubby or hair-like, with branched, fibrous structures.
Crustose Lichen. Crustose lichens cling to the surface they are on. These are common on rocks and tree bark.
Foliose Lichen. Foliose lichens have a leafy appearance even though these are not true leaves.
Fruticose Lichen. Fruticose lichens are often heavily branched and look more like a small shrub.
Common Species of Lichen in Texas
Common Species of Lichen in Texas
Because lichens can withstand long dry periods they are ideally suited for the climate of central Texas. As a result we have many species here in the Austin area. Below are some of the common species in this area. You should be able to identify the genera of these species.
Fruticose
Fruticose
Genus Teloschistes. The two most common species of fruticose lichen in central Texas are closely relates species, Slender Orange-Bush (above) and Golden-eye Lichen (below). The orange "cups" are very distinctive and make them easy to recognize in the genus Teloschistes. The difference is that the Slender Orange Bush (Teloschistes exilis) lacks the "eyelashes" around the cup that exist in the Golden-eye Lichen (Telochistes chrysophthalmus).
Foliose
Foliose
Genus Flavoparmelia. This is a Common Greenshield Lichen (Flavoparmelia caperata). It can vary in color from a light blue to green. This is a foliose lichen that is commonly found on the trunk and stems of various trees.
Genus Ramalina. This is called a Cartilage Lichen (Ramalina celastri). It is a foliose lichen that has a very leafy look to it. If you look closely you can see the ascocarps on the surface of this "leaf" indicating that it is a fungus rather than a plant.
Crustose
Crustose
Genus Rhizocarpon. This is a common crustose lichen. It is often found on the exposed rocks.
Lab Activity: Identifying Lichen Body Forms
Lab Activity: Identifying Lichen Body Forms
Materials
Materials
Stems or branches containing multiple lichen types
Additional loose lichen specimens
Reference images of crustose, foliose, and fruticose lichens
Dissecting microscope (optional)
Note: Handle specimens carefully to avoid breaking delicate structures.
Instructions
Instructions
Examine the lichen specimens attached to the stems or branches.
Compare the overall structure of each lichen thallus.
Identify the three major lichen body forms:
Crustose – thin crust tightly attached to the surface and difficult to remove.
Foliose – flattened, leaf-like lobes with a distinguishable upper and lower surface.
Fruticose – branching or shrubby growth extending outward from the substrate.
Identify examples of each body form among the specimens provided.
Examine the additional loose specimens and determine which body form each represents.
Use your observations to answer the worksheet questions about lichen morphology.
Use the common Texas lichen key to determine if you can identify any of them that you are observing.
Clean Up
Clean Up
Return all specimens to the tray or container.
Leave the station organized for the next group.
Reproduction
Reproduction
Lichens reproduce in two primary ways:
1. Asexual Reproduction (Primary Method)
Most lichens reproduce by fragmentation of their thallus (body).
Many also produce soredia—tiny clusters of fungal hyphae surrounding algal cells—which are carried by wind, water, or animals to colonize new locations.
2. Sexual Reproduction (Fungal Partner Only)
While the fungal component may produce sexual spores (ascomycete asci or basidiomycete basidia), these spores must find a compatible photobiont to form a new lichen, making this strategy less common.
This is a diagram of the typical organization of algae within the fungal hypha of a lichen. You can see the ascocarp of this fungus reminding us that most lichens are made up of ascomycete fungi. The scanning electron micrograph image demonstrates the close association of hypha and algal cells.
Algal cells are embedded in the thalus of a lichen surrounded by hyphae.
Lab Activity: Lichen Thallus Cross Section (Prepared Slide)
Lab Activity: Lichen Thallus Cross Section (Prepared Slide)
Materials
Materials
Prepared slide of a lichen cross section
Compound microscope
Note: Handle slides carefully.
Instructions
Instructions
Examine the prepared slide under the microscope.
Identify the fungal tissue forming the structure of the lichen.
Locate the green algal cells embedded within the fungal layers.
Observe how the fungal hyphae surround and support the algal partner.
Locate the ascocarp and identify the asci, which contain fungal spores.
Use the slide to answer the worksheet questions about the symbiotic relationship between the fungus and the photosynthetic partner.
(In most lichens the fungal partner is an ascomycete that produces spores in asci.)
Clean Up
Clean Up
Return the prepared slide to the slide box.
Turn off the microscope and leave the station organized.
New Discoveries in Lichen Biology
New Discoveries in Lichen Biology
Recent studies suggest lichens are far more complex than previously thought. Many lichens may involve three or more symbiotic partners—including multiple fungal species, secondary bacterial communities, and additional cyanobacterial partners—forming miniature ecosystems rather than simple two-partner relationships.
Bioluminescent Fungi
Bioluminescent Fungi
Bioluminescent fungi are species capable of producing natural light through a biochemical reaction involving luciferin (a light-emitting compound), the enzyme luciferase, oxygen, and ATP. This reaction creates a greenish glow that can be seen in complete darkness. Over 80 species of glowing fungi have been described, almost all belonging to the phylum Basidiomycota.
Ecology and Function
Ecology and Function
Bioluminescent fungi are most common in tropical and subtropical forests, though some species occur in temperate regions. The majority live as saprotrophs, breaking down dead wood and recycling nutrients.
While the exact evolutionary function of fungal bioluminescence is still debated, two major hypotheses dominate:
Spore Dispersal Hypothesis
The glow attracts insects like flies, beetles, and springtails at night.
These insects land on the fruiting bodies and inadvertently transport spores to new locations.
Byproduct Hypothesis
The glow may simply be a byproduct of metabolic reactions tied to reactive oxygen detoxification.
However, evidence increasingly supports the idea that the glow benefits the fungus ecologically.
Examples of Bioluminescent Fungi
Examples of Bioluminescent Fungi
Genus Mycena – The largest group of glowing fungi, with many species producing faint light in the cap and gills.
Armillaria mellea (Honey Fungus) – Its mycelium glows beneath tree bark, earning it the nickname “foxfire.”
Panellus stipticus – Known for bright luminescence in both the fruiting body and mycelium, commonly studied in labs.
Omphalotus olearius (Jack-o’-Lantern Mushroom) – Produces a bright glow from its gills; highly toxic despite its appealing appearance.
Mycena chlorophos
Armillaria mellea (Honey Fungus)
Panellus stipticus
Omphalotus olearius (Jack-o'-Lantern)
Biochemistry of the Glow
Biochemistry of the Glow
The fungal glow results from a luciferin-luciferase reaction:
Luciferin → a small molecule that emits photons when oxidized.
Luciferase → the enzyme that catalyzes the oxidation reaction.
The reaction requires ATP and oxygen and produces oxyluciferin + light.
This biochemical pathway is distinct from fireflies and marine bioluminescence, meaning fungal glowing likely evolved independently.
Fungal Bioluminescence Pathway
Applications and Research
Applications and Research
Bioluminescent fungi are attracting attention in biotechnology and ecology:
Environmental Monitoring → Potentially used as bioindicators in forest ecosystems.
Biotechnology → Genes responsible for fungal bioluminescence have been successfully transferred into plants to create glowing houseplants.
Evolutionary Studies → Understanding why multiple unrelated lineages evolved bioluminescence sheds light on convergent evolution.
Glowing in the Dark – Why?
Glowing in the Dark – Why?
Bioluminescent fungi produce their own natural light through a chemical reaction involving luciferin, luciferase, oxygen, and ATP. These fungi emit a greenish glow that is visible in total darkness. It begs the question, why do they glow? The debate is ongoing but there are a couple of leading hypotheses.
Why Do They Glow?
Spore Dispersal Hypothesis → The glow attracts insects at night, which carry spores to new habitats.
Byproduct Hypothesis → The glow may help detoxify oxygen radicals, though growing evidence supports an ecological purpose.
Fun Fact
Some species, like Mycena, are so bright that entire forest floors appear to shimmer at night during peak fruiting seasons.
Lab Activity: Bioluminescent Fungi
Lab Activity: Bioluminescent Fungi
Materials
Materials
Images or video of bioluminescent fungi
Brief information sheet on fungal bioluminescence.
Instructions
Instructions
Observe the images or video of bioluminescent fungi provided at the station.
Identify the parts of the fungus that appear to produce light.
Compare the structure of these fungi to the mushrooms you observed in the Basidiomycota station.
Consider possible ecological reasons why a fungus might produce light.
Use the information provided to answer the worksheet questions about fungal bioluminescence.
Clean Up
Clean Up
Leave the images and materials at the station for the next group.
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